The nature of the immunogen responsible for the ease or difficulty in tolerance induction to HGG in DBA/2 and Balb/C mice will be studied by analyzing the ability of macrophages from these strains to bind various immunoglobulin subclasses. A rosetting technique involving red cells coupled with various IgG subclass myelomas will be used. The nature of suppressions to azobenzenearsonate sensitivity will be directed towards determining the nature of the cell involved. A passive transfer system in inbred rats will be developed to study suppression of in vitro lymphocyte proliferation and in vivo helper effects in antibody production. The nature of the T cell responsible for cutaneous basophil hypersensitivity and its ability to release chemotactic substances which attract basophils will be sought in passive transfer systems. BIBLIOGRAPHIC REFERENCES: Lukic, M.L., Wortis, H.H., and Leskowitz, S. A gene locus affecting tolerance to BGG in mice. Cellular Immunol. 15: 457, 1975. Stadecker, M., and Leskowitz, S. Genetic control of cutaneous basophil hypersensitivity. J. Exp. Med. 143: 206, 1976.